Causes of melanoma

The exact cause of melanoma is not known, although most cases are closely linked to the effects of ultraviolet (UV) light on the skin.

What is cancer?

The body is made up of millions of different types of cells. Cancer happens when some cells multiply in an abnormal way. When cancer affects organs and solid tissues, it causes a growth called a tumour to form. Cancer can occur in any part of the body.

It is not clear why cells sometimes multiply abnormally.

How does cancer spread?

Left untreated, cancer can quickly grow and spread, either in the skin or the blood, or to other parts of the body. This usually happens through the lymphatic system.

The lymphatic system is a series of glands that spread throughout your body and link together in a similar way to the blood circulation system. The lymph glands produce many of the cells needed by your immune system.

If the cancer reaches your lymphatic system, it can spread to any other part of your body, including your bones, blood and organs.


In most cases, it is thought melanomas are caused by exposure to sunlight. Sunlight contains UV light that can affect the skin.

There are two main types of UV – ultraviolet A (UVA) and ultraviolet B (UVB). Both UVA and UVB damage skin over time, making it more likely for skin cancers (including melanomas) to develop.

Artificial sources of light, such as sunlamps and tanning beds, may also increase your risk of developing melanoma skin cancer.

However, not all melanomas are linked with exposure to UV light and they can appear on areas of skin that are rarely exposed.

Increased risk

Factors that increase your risk of developing melanoma include:

  • pale skin that tends to burn and not tan easily
  • a family member who has had melanoma
  • red or blonde hair
  • blue eyes
  • age
  • a large number of moles
  • a large number of freckles
  • a condition that suppresses your immune system, such as HIV
  • medicines that suppress your immune system (immunosuppressants), commonly used after organ transplants

All of the above risk factors make your skin more sensitive to the effects of the sun.

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